Backlash is a major source of undesirable noise in gear assemblies. Backlash allows the teeth of one gear to, momentarily, lose contact with the teeth of the mating gear. The noise is generated, by a tooth-to-tooth impact that occurs, when the teeth of the two gears reestablish contact with one another. The momentary loss of contact between meshing teeth often happens during specific operating conditions of the gear assembly. Such conditions include; during excessive vibration and during directional changes of at least one of the gears, for example.
Typical gear assembly design practices rely upon geometric tolerancing to position meshed gears in operable relation to one another. However, due to variation in build tolerances and component wear, clearances have to exist between the teeth of meshed gears, thereby allowing backlash, and the undesirable noise associated with it to persist.
In addition to noise, clearances may also cause degradation in operational efficiency of the meshed gears due to the contact point between the gear teeth deviating from the preferred design location. The contact force between the meshed gears is one major cause of this deviation. The contact force includes a radial component that acts in a direction to separate the gears from one another. Consequently, any clearances in the meshed gears may be biased to increase the distance between the axes of the gears resulting in reduced meshing engagement. The reduced meshing engagement alters the contact point between the meshed gears, which may result in a loss of efficiency and strength.
Typical methods employed to minimize these clearances include both springs and dampers. The springs are used to bias the gears toward one another in an attempt to assure that the gears are fully meshed together regardless of the clearances. However, the spring forces necessary to maintain the gears in full meshed engagement cause a loss in efficiency due to an increase in friction between the meshed gear teeth. Dampers are employed to allow for use of springs with lesser biasing forces. Such lighter force springs create a preload when the gears are not operationally engaged. A high damper stiffness is used to counter the separational forces of the meshed gears and to thereby reduce the backlash and loss of efficiency that results from the gears moving away from one another.
During operation, the load put on the dampers varies significantly as the operational conditions of the meshing gears change. For the dampers to successfully counter these varying forces the damper coefficients of the dampers must vary depending on the operating conditions of the gear assembly. It may be possible to create variable dampers, and algorithms to control them, based upon the operational conditions of the meshed gears. However, such systems may be highly complex, costly, and still have negative effects on the operational efficiency of the assembly.
Accordingly, there is a need in the art for a concept that automatically eliminates backlash and maintains a desired positional relationship of the meshing gears regardless of the operating conditions of the meshed gears.